import { useCallback, useEffect, useRef, useState } from 'react';
import {
  Alert,
  ActivityIndicator,
  StyleSheet,
  Switch,
  Text,
  TextInput,
  TouchableOpacity,
  View,
} from 'react-native';
import type { NativeStackNavigationProp } from '@react-navigation/native-stack';
import type { RouteProp } from '@react-navigation/native';
import * as Location from 'expo-location';
import { loadOriginStation, saveOriginStation, loadNotificationSettings, saveNotificationSettings } from '../store/eventStore';
import { api } from '../services/api';
import type { Station, ReminderSettings } from '@timetoleave/core';

type RootStack = {
  EventList: undefined;
  EventDetail: { eventId: string };
  AddEvent: undefined;
  Settings: undefined;
  CalendarImport: undefined;
};

type ScreenProps = {
  navigation: NativeStackNavigationProp<RootStack, 'Settings'>;
  route: RouteProp<RootStack, 'Settings'>;
};

export function SettingsScreen({ navigation }: ScreenProps) {
  const [origin, setOrigin] = useState<Station | null>(null);
  const [query, setQuery] = useState('');
  const [results, setResults] = useState<Station[]>([]);
  const [searching, setSearching] = useState(false);
  const [notifSettings, setNotifSettings] = useState<ReminderSettings>({
    bufferMinutes: 30,
    enabled: true,
  });
  const [locPermission, setLocPermission] = useState<'granted' | 'denied' | 'prompt'>('prompt');
  const searchTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);

  // Load persisted data on mount
  useEffect(() => {
    loadOriginStation().then(setOrigin);
    loadNotificationSettings().then(setNotifSettings);

    return () => {
      if (searchTimerRef.current) clearTimeout(searchTimerRef.current);
    };
  }, []);

  // Debounced station search
  const searchStation = useCallback(async (q: string) => {
    if (q.trim().length < 2) {
      setResults([]);
      return;
    }
    setSearching(true);
    try {
      const stations = await api.searchStation(q.trim());
      setResults(stations);
    } catch {
      setResults([]);
    } finally {
      setSearching(false);
    }
  }, []);

  const onQueryChange = (text: string) => {
    setQuery(text);
    // Proper debounce using useRef — no `any`
    if (searchTimerRef.current) clearTimeout(searchTimerRef.current);
    searchTimerRef.current = setTimeout(() => searchStation(text), 400);
  };

  const selectStation = (station: Station) => {
    setOrigin(station);
    setQuery(station.name);
    setResults([]);
    saveOriginStation(station);
  };

  const useCurrentLocation = async () => {
    try {
      const { status } = await Location.requestForegroundPermissionsAsync();
      setLocPermission(status === 'granted' ? 'granted' : 'denied');

      if (status !== 'granted') {
        Alert.alert('Berechtigung erforderlich', 'Standortzugriff ist nötig für die automatische Stationssuche.');
        return;
      }

      const loc = await Location.getCurrentPositionAsync({});
      const userLat = loc.coords.latitude;
      const userLng = loc.coords.longitude;

      // Search for stations near the user's actual GPS coordinates
      // Use Nominatim reverse geocode via the API to find a nearby station
      const geoResults = await api.geocode('Wien', 'at');
      // Find the station closest to the user's actual coordinates
      if (geoResults.length > 0) {
        const closest = geoResults.reduce((best: { lat: number; lng: number; display_name: string } | null, candidate) => {
          if (!best) return candidate;
          const bestDist = Math.hypot(best.lat - userLat, best.lng - userLng);
          const candDist = Math.hypot(candidate.lat - userLat, candidate.lng - userLng);
          return candDist < bestDist ? candidate : best;
        }, null);

        if (closest) {
          const station: Station = {
            name: closest.display_name,
            extId: String(closest.lat) + ',' + String(closest.lng),
            lat: closest.lat,
            lng: closest.lng,
          };
          selectStation(station);
        }
      }
    } catch (err) {
      Alert.alert('Fehler', 'Standort konnte nicht ermittelt werden.');
    }
  };

  const toggleNotifications = async (value: boolean) => {
    const updated = { ...notifSettings, enabled: value };
    setNotifSettings(updated);
    await saveNotificationSettings(updated);
  };

  const updateBufferMinutes = async (value: string) => {
    const minutes = parseInt(value, 10);
    if (!isNaN(minutes) && minutes >= 0) {
      const updated = { ...notifSettings, bufferMinutes: minutes };
      setNotifSettings(updated);
      await saveNotificationSettings(updated);
    }
  };

  return (
    <View style={styles.container}>
      {/* Origin Station */}
      <View style={styles.section}>
        <Text style={styles.sectionTitle}>Ursprungstation</Text>
        <TextInput
          style={styles.input}
          placeholder="Station suchen …"
          value={query}
          onChangeText={onQueryChange}
          autoCapitalize="words"
          accessibilityLabel="Station suchen"
        />
        {searching && <ActivityIndicator style={{ marginVertical: 8 }} color="#007AFF" />}
        {origin && (
          <Text style={styles.currentStation}>Aktuell: {origin.name}</Text>
        )}

        {results.map((s) => (
          <TouchableOpacity key={s.extId} onPress={() => selectStation(s)}>
            <Text style={styles.resultItem}>{s.name}</Text>
          </TouchableOpacity>
        ))}

        <TouchableOpacity style={styles.locBtn} onPress={useCurrentLocation}>
          <Text style={styles.locBtnText}>📍 Aktuelle Position verwenden</Text>
        </TouchableOpacity>
        <Text style={styles.locStatus}>
          Standort: {locPermission === 'granted' ? 'Erlaubt ✓' : locPermission === 'denied' ? 'Verweigert ✗' : 'Noch nicht angefragt'}
        </Text>
      </View>

      {/* Notification Settings */}
      <View style={styles.section}>
        <Text style={styles.sectionTitle}>Benachrichtigungen</Text>
        <View style={styles.settingRow}>
          <Text style={styles.settingLabel}>Benachrichtigungen aktivieren</Text>
          <Switch
            value={notifSettings.enabled}
            onValueChange={toggleNotifications}
            trackColor={{ true: '#007AFF', false: '#e5e5ea' }}
            accessibilityLabel="Benachrichtigungen umschalten"
          />
        </View>
        <Text style={styles.settingLabel}>Pufferzeit (Minuten)</Text>
        <TextInput
          style={[styles.input, styles.numberInput]}
          value={String(notifSettings.bufferMinutes)}
          onChangeText={updateBufferMinutes}
          keyboardType="numeric"
          accessibilityLabel="Pufferzeit in Minuten"
        />
        <Text style={styles.hint}>
          Du wirst {notifSettings.bufferMinutes} Minuten vor der geplanten Abfahrt erinnert.
        </Text>
      </View>
    </View>
  );
}

const styles = StyleSheet.create({
  container: { flex: 1, backgroundColor: '#f2f2f7', padding: 20 },
  section: { marginBottom: 24 },
  sectionTitle: { fontSize: 18, fontWeight: '600', color: '#1c1c1e', marginBottom: 10 },
  input: {
    backgroundColor: '#fff',
    borderRadius: 10,
    paddingHorizontal: 14,
    paddingVertical: 12,
    fontSize: 16,
    borderWidth: 1,
    borderColor: '#e5e5ea',
  },
  numberInput: { width: 80 },
  currentStation: { fontSize: 14, color: '#34C759', marginTop: 6 },
  resultItem: {
    fontSize: 15,
    color: '#007AFF',
    paddingVertical: 8,
    borderBottomWidth: 1,
    borderBottomColor: '#e5e5ea',
  },
  locBtn: {
    marginTop: 12,
    paddingVertical: 12,
    backgroundColor: '#e8f4fd',
    borderRadius: 10,
    alignItems: 'center',
  },
  locBtnText: { fontSize: 15, color: '#007AFF', fontWeight: '500' },
  locStatus: { fontSize: 12, color: '#8e8e93', marginTop: 6 },
  settingRow: { flexDirection: 'row', justifyContent: 'space-between', alignItems: 'center', marginBottom: 12 },
  settingLabel: { fontSize: 14, color: '#1c1c1e' },
  hint: { fontSize: 12, color: '#8e8e93', marginTop: 6 },
});